(a) Field of the Invention
The present invention relates to an improvement of plastic molding of a semiconductor device.
(b) Description of the Prior Art
In general, semiconductor devices mounted in electronic wristwatches or on memory boards have a structure wherein semiconductor elements are directly mounted on printed circuit boards or ceramic boards. In order to protect the semiconductor elements from external stress or external humidity, they are mounted on the board, and the bonding wires (gold or aluminum thin wires) electrically connect the semiconductor elements with the board wiring pattern. The semiconductor elements mounted on the board are molded by a sealing resin such as epoxy resin or silicone resin. The resin sealing is performed by using a liquid resin or a solid resin. When the solid resin is used, it is heated and melted.
When the liquid resin is used, however, the injection operation cannot be fully automated, and the viscosity of the resin cannot be properly controlled. For these disadvantages, in general, a solid resin is used as shown in FIGS. 1(A) to 1(C). Referring to FIG. 1(A), a desired semiconductor element 3 is mounted on a predetermined region of a circuit board 2 having a wiring pattern 1, and bonding wires 4, are bonded between the semiconductor element 3 and the wiring pattern 1. A frame 5 for surrounding the wiring pattern 1 connected to the semiconductor element 3 through the bonding wires 4 is fixed by an adhesive 8 on the circuit board 2. As shown in FIG. 1(B), a sealing resin block 6 having a predetermined size is placed in the frame 5. Heat is applied to the resin block 6 to form a molded resin portion 6' which seals the semiconductor element 3 and the like, as shown in FIG. 1(C). As a result, a semiconductor device 7 is prepared.
However, in the method using the solid resin block, the resin block 6 is dropped into the frame 5 for a considerably long distance, so that a great impact or load acts on the semiconductor element 3 and the bonding wires 4. As a result, the bonding wires 4 tend to be disconnected or peel off from the bonded metal portions. In order to prevent these problems, it has been proposed to divide the resin block 6 into several pieces. However, in this case, the steps of dividing a resin block into several pieces and of placing the divided pieces into the frame must be added, thereby degrading operability.